1. Field of the Invention
The present invention relates to a pump to spray fuel at a high pressure into combustion chambers of an engine and, more particularly, a variable-delivery high-pressure fuel pump to pressurize, meter a fuel and then deliver the metered fuel to the combustion chambers.
2. Description of the Prior Art
For the variable-delivery high-pressure fuel pumps, generally, two types of pumps have been developed one of that is a high-pressure fuel pump 80 of inlet port-metering system, as shown in FIG. 9. It has an inlet port valve 81 for regulating an inflow rate of fuel into a cylinder to control a metered amount of fuel discharged. The other is a high-pressure fuel pump 90 of a system that is termed pre-stroke control, as shown in FIG. 10, where an inlet port valve 91 is controlled according to the pre-stroke way.
The high-pressure fuel pump 80 shown in FIG. 9 is a type of fuel pump to spray the pressurized fuel at a high pressure into the combustion chambers of the engine, in which a fuel introduced through a fuel inlet passage 82 when the inlet port valve 81 is kept open is pressurized in a pump chamber 85 by the action of a reciprocating pump plunger 84 actuated by an eccentric cam 83, which is driven by a power-take-off shaft of the engine. The pressurized fuel is then delivered to either a common fuel rail or injectors through a fuel discharge passage 86. According to the type as described just above, the metered amount of fuel discharged is determined depending on the inflow rate of fuel that flows through a valve seat for a pre-selected time during which the inlet port valve 81 is kept open.
In contrast, the high-pressure fuel pump 90 illustrated in FIG. 10 operates with such systems that the inlet port valve remains open after the bottom top center of the pump plunger for a short time of delay until a volume confined between the pump plunger and its associated cylinder reaches a desired amount of fuel to be discharged. The instant the desired amount of fuel is reached in the pump chamber, the inlet port valve is closed and the metered amount of fuel, which has been trapped in the pump chamber defined by the cylinder on the plunger, is delivered out of the pump chamber. Thus, excess fuel in the pump chamber is left returned through the inlet port valve until the pump chamber defined by the cylinder on the plunger is made reduced in volume to the desired amount of fuel to be discharged.
In the high-pressure fuel pump 90, the plunger 94 moves up and down as a cam 93 rotates, thereby varying the volume in the pump chamber 95. On descendent movement of the plunger 94, the pump chamber 95 is increased in volume while reduced in pressure, resulting in opening the inlet port valve 91 of a solenoid-actuated valve to admit the fuel into the pump chamber through a fuel inlet line 92. The inflowing fuel is not under the high pressure, but at a relatively low-pressure anticipated by a low-pressure supply pump. The pump chamber is initially sufficient large in volume compared with the desired amount of fuel to be discharged. As the cam 93 starts to rotate, the plunger 94 lifts to reduce the pump chamber 95 in its volume with the inlet port valve 91 still remaining open. Thus, the fuel admitted in the pump chamber 95 is partly forced to return through the inlet port valve 91 to the fuel inlet passage 92. The instant the amount of fuel in the pump chamber 95 has reached the desired amount of fuel, the inlet port valve 91 is closed. Thereafter as the plunger 94 continues to move upwardly, the fuel metered in the pump chamber 95 is forcible discharged to a fuel delivery port 96.
Disclosed in Japanese Patent Laid-Open No. 257533/1994 is a prior fuel-injection pump of pre-stroke control system, in which a back-pressure chamber supplied with a low-pressure fuel is provided behind a main valve body partly forming walls of a pump chamber. The fuel pressure in the back-pressure chamber is controlled by opening and closing between the back-pressure chamber and a subsidiary valve chamber by the action of a solenoid-actuated subsidiary valve, which is held for sliding movement in the subsidiary valve chamber. A piston section of the main valve body moves in a reciprocating manner in compliance with the combination of an urging force of a main valve spring and a pressure difference between the back-pressure chamber and an area in a main valve chamber, which communicates with a fuel passage or is exposed to the pump chamber, to thereby let the main valve body open and close between the back-pressure chamber and the subsidiary valve chamber. No fuel in the pump chamber is discharged backwards to the fuel passage at an earlier portion of lift of the plunger. Energization of the solenoid-actuated valve, nevertheless, regulates the timing for closure of the main valve body that allows the pressure to escape from the back-pressure chamber. This controls the effective stroke of the plunger after the back-pressure chamber has been disconnected from the pump chamber in a compressively forcing phase of the plunger.
Another conventional high-pressure fuel-injection pump of pre-stroke control system is disclosed in Japanese Patent No. 2,690,734. In accordance with this prior high-pressure fuel-injection pump, electric conduction of a solenoid-actuated valve makes a valve body block up a passage formed between the valve body and its valve seat for interconnecting a pump chamber with a low-pressure passage. Fuel in the pump chamber is raised in pressure by means of a compression member and then discharged to a common fuel-rail through a delivery port. Varying an electric conductive duration to the solenoid-actuated valve results in controlling the amount of fuel delivered to the common fuel-rail. The solenoid-actuated valve includes an outwardly-opening poppet-type valve body that is exposed at its entire lower surface against the pressure created in the pump chamber. Thus, the fuel pressure created in the pump chamber acts on the valve body as a motive force to effectively urge the valve body against its valve seat at closure event, in addition to the electromagnetic attractive force of the solenoid-actuated valve, to thereby aid the solenoid-actuated valve in ensuring the intensified closure power, resulting in keeping the pressure against any leakage past the valve at the closure event.
With most high-pressure fuel pumps of inlet port-metering system, on the other hand, a negative pressure developed ahead of the inlet port valve raises a major disadvantage of unsteady operation of the inlet port valve, which might occur due to cavitation or a sudden change in pressure. It has been thus required to eliminate the possible negative pressure ahead of the inlet port valve or keep the pressure ahead of the valve on any positive pressure. This, however, makes the inlet port valve complicated in structure. In conventional flow rate control of pre-stroke system to drive directly the inlet port valve connecting the pump chamber with the low-pressure side, moreover, the inlet port valve has to be actuated against the fuel pressure elevated up to a high pressure in the pump chamber and, therefore, it is inevitably required to make large the elastic force of a spring and the electromagnetic force of a solenoid-actuated valve to operate the inlet port valve. This leads to the large size of the solenoid-actuated valve, which might contribute to plague drawbacks of noise pollution and power-hungry consumption. In contrast, where the inlet port valve is operated, indirectly with making use of the low pressure fuel, by the energization of the solenoid-actuated valve, a control mechanism of using the low-pressure fuel is arranged between the solenoid-actuated valve and the inlet port valve. This design may likewise result in a bulky high-pressure fuel pump. With either system of direct or indirect operation of the inlet port valve, the drawbacks are the same as described just above: the solenoid-actuated valve becomes bulky in size while the control mechanism for the inlet port valve is made large-sized and complicated. In addition, the prior inlet port valve is apt to become unsteady in its operation to cause a jump in the amount of fuel delivered or an unfavorable problem of the marked pressure fluctuation occurring in the amount of fuel delivered out of the high-pressure pump. To cope with this, a damping mechanism is required to make steady the operation of the inlet port valve. Nevertheless, this causes the disadvantageous increase in the production cost of the high-pressure fuel pump.
Moreover, the high-pressure fuel pumps of pre-stroke control system operate usually to allow the fuel returning to the fuel-supply pump that may be considered the primary side. Accordingly, the fuel-supply pressure, or 3 to 8kg/ cm2, disappears in pumping loss. The solenoid-actuated valve for the inlet port valve 91 sometimes raises another problem in which the inlet port valve when assembled renders the fuel pump too large in height, thereby making it even tougher to mount the inlet port valve on the engine. That is to say, the inlet port valve 91 is needed to provide the great attractive or compressive force to compress the fuel up to the high pressure. This leads to the large size of windings or coils with the result of making the solenoid-actuated valve bulky.
For providing the solenoid-actuated valve compact in structure and improved in noise pollution as well as power consumption, accordingly, it will be favorable for the high-pressure pumps to let the inlet port valve operate with making use of the pressure inherent in the fuel pressurized at a low pressure by the fuel-supply pump, instead of directly operating the inlet port valve by the energization of the solenoid-actuated valve for intermittently opening and blocking the fuel passage of low-pressure side to the pump chamber. Directly using the low-pressure fuel for opening and closure of inlet port valve, moreover, results in making as compact as possible in size the valve-operating mechanism for the inlet port valve, which is arranged between the solenoid-actuated valve and the inlet port valve, whereby the high-pressure fuel pump may be designed reduced in its overall height.
To overcome the problems as set forth above, therefore, a primary object of the present invention is to provide a high-pressure fuel pump having a solenoid-actuated valve of smaller equivalent size whereby a control valve is made compact in structure, reduced in noise under operation as well as diminished in power consumption. Thus, the present invention may make it easy to mount the high-pressure fuel pump on the engine.
The present invention is concerned with a variable-delivery high-pressure fuel pump comprising, a pump chamber varying in volume as a plunger moves in and out, an inlet port valve forming at a one end thereof a part of chamber walls of the pump chamber, the inlet port valve being opened when a low-pressure fuel is admitted into the pump chamber from a fuel inlet passage, while being closed when the admitted fuel is delivered out of the pump chamber, a control chamber defined on an opposing end of the inlet port valve to receive therein the low-pressure fuel applied through the fuel inlet passage, and a control valve for intermittently opening and blocking a fluid communication between the control chamber and the fuel inlet passage.
In accordance with the high-pressure fuel pump constructed as described above, the control chamber is formed on the top end of the inlet port valve and controlled in the pre-stroke way as the control valve is turned on and off. The fuel pressure of a low-pressure fuel applied with the fuel-supply pump is introduced into the control chamber, where the fuel pressure acts hydraulically on the inlet port valve, either directly or indirectly through any simple means. Moreover, the control chamber, when isolated with the closure of the control valve, may be made a hydraulic stiffness. Thus, the inlet port valve remains opened owing to the stiffness of the control chamber even during the plunger moves in or upwards. This allows the fuel in the pump chamber to flow backwards into the fuel inlet passage so that no fuel may be delivered at high pressure. In the event the fuel in the pump chamber is flowing backwards into the fuel inlet passage according to the upward movement of the plunger, the instant the control valve is opened, the inlet port valve is relieved from the pressure acting in the direction to open the inlet port valve and, thus moved to its closure position. With the inlet port valve coming in closure, the fuel pressure in the pump chamber is elevated up to a high pressure. Thereafter, the fuel pressure in the pump chamber begins to rise and the fuel intensified in fuel pressure is delivered out of the pump chamber, past the fuel delivery line during the delivery stroke of the plunger. Control of the timing the control valve is made open results in controlling the timing for closure of the inlet port valve to thereby regulate the amount of fuel delivered out of the pump chamber. The timing the inlet port valve is closed depends on any pressure balance among the intake pressure, resilient force of the compression spring for the inlet port valve and hydraulic pressure in the control chamber. During the plunger is moving in or upwards to thereby boost the fuel pressure in the pump chamber, the inlet port valve remains open against the force owing to the fuel pressure in the pump chamber acting in the direction of pushing upwards the inlet port valve.
In an aspect of the present invention, a variable-delivery high-pressure fuel pump is provided, wherein the inlet port valve is of a poppet-type valve made with a valve head having a valve face moving off and reseating against a valve seat in the pump chamber, and a valve stem integral with the valve head and extended out of the pump chamber into the control chamber. As an alternative, the inlet port valve is of a poppet-type valve made with a valve head having a valve face moving off and reseating against a valve seat in the pump chamber, and a valve stem integral with the valve head and extended out of the pump chamber, and the control chamber contains therein an intermediate piston that comes in abutment with the valve stem of the inlet port valve. With the modification the intermediate piston is incorporated, the control chamber is defined on the top of the intermediate piston instead of the valve stem of the inlet port valve.
In a design where the intermediate piston is made separately from the inlet port valve and they are assembled together, any measure should be adopted at the face-to-face abutment between the intermediate piston and the valve stem of the inlet port valve to help ensure the steady operation of them at high speed. To this end, the intermediate piston is formed in a concavity at lengthwise one end face thereof kept on abutment with valve stem, which is formed in a convexity at lengthwise one end thereof kept on abutment with the intermediate piston. In this case, moreover, the concavity on the intermediate piston and the convexity on the valve stem are of parts of a concave shpericity and a convex shpericity, respectively, and the concave shpericity is made larger in its radius of curvature than the convex shpericity.
In another aspect of the present invention, a variable-delivery high-pressure fuel pump is provided, wherein the control valve is of a solenoid-actuated valve. Moreover, it is preferred that the control valve is of a two-way valve. The solenoid-actuated valve may control the fuel pressure in the pump chamber with high response characteristic in compliance with control signals issued from any electronic control unit. The closure of the control valve lets the control chamber isolate fluid-tightly. In contrast, opening the control valve allows the control chamber to make fluid communication with the low-pressure side.
In another aspect of the present invention, a variable-delivery high-pressure fuel pump is provided, which regulates a timing for opening the control valve as the plunger moves from bottom dead center to top dead center of its stroke, to thereby control a timing for closure of the inlet port valve, resulting in metering an amount of fuel delivered out of the pump chamber. Control of the timing a signal to energize the control valve is turned off results in controlling the timing the position of the control valve causes the control chamber to open, that is, the timing the inlet port valve is made closed off and at the same time the fuel delivery out of the pump chamber begins. Possible control of the timing the fuel delivery begins makes it possible to meter the amount of fuel delivered out of the pump chamber per very delivery cycle of the fuel pump.
The high-pressure fuel pump of the present invention constructed as described above makes the inlet port valve open and close by the effect of low-pressure fuel applied from the fuel-supply pump. Only the control valve is, thus, sufficient to regulate the fuel supply of low-pressure fuel to the control chamber and the fuel relief out of the control chamber. As a result, smaller equivalent size of the control valve is realized with the reduction of noise on operation as well as the less consumption of electric power. Moreover, because of smaller equivalent size, it may become possible to make easy mount the fuel pump on the engine, according to the modification as to the arrangement of the fuel pump.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.